WAEC 2020 · Paper 1 · Q22

Quadratics & their graphs
Linear & simultaneous equations

A man is five times as old as his son. In four years' time, the product of their ages would be 340. If the son's age is $y$ , express the product of their ages in terms of $y$ .

Worked solution (try it first)

The man is $5y$ now.
In four years the son is $y + 4$ and the man is $5y + 4$ .
Their product then is 340: $(5y + 4)(y + 4) = 340$ .
Expand: $5y^2 + 20y + 4y + 16 = 340$ , so $5y^2 + 24y + 16 = 340$ .
Subtract 340: $5y^2 + 24y - 324 = 0$ , option D.

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